二つの花崗岩山地小流域におけるミネラルの収支についての報告

Abstract

1. 前報に引き続いて, 花陶岩山地の二つの小流域についてミネラルの収支の点から, 1972年4月より, 1973年3月までの一年間, 比較をおこなった。実験期間中, 二流域の降水, および流出水について, 五種のミネラルの分析, 定量をおこない, この流域の移入量, 移出量とした。実験流域は, 前報におなじ桐生流域と川向流域である。2. 実験期間中, 降水量について, 桐生では1811. 0mm, 川向では1693. 0mmとなり, 流出量は, 桐生1478. 8mm, 川向920. 9mm, となった。流出率で桐生の値が例年値より高かった。3. 溶存ミネラル成分のうち, それぞれの流域の漢流水に含まれるミネラルの濃度は, 二流域で, 平均値では, 大きな差はみとめられなかったが, 一般に桐生の方が, 変動幅は, 川向より大きかった。渓流水のミネラル濃度の季節変化は, 桐生では多くのミネラルで様子がはっきりしなかったが, 川向では変動幅が小さく, 夏期に濃度が高くなり, 冬期・春期にかけて低くなるようであった。また二流域で, 増水直後にNaの濃度の低下, Mgに濃度の上昇がみられた。4. 収支計算の結果, 桐生でP以外のミネラルで支出が収入をうわまわったが, 川向ではPとCaで収入が大きく, K, Naでは支出がうわまわり, Mgは, ほぼ, 収入・支出がつりあった。二流域で各ミネラルの収入量は, ほぼ同じであると思えるのに, 全体として, 桐生の支出が川向のそれの約2倍になった。

1. The mineral budgets of two small catchments in granite region at Kiryu and Kawamukai Experimental catchments located in Otsu city, Shiga Prefecture were analyzed during the period of April 1972--March 1973. The catchments are characterized by similarities of climatic conditions, edaphic substrates of bedrock and the differences of vegetational development. 2. During this one year period, the precipitation inputs were 1811.0 and 1693.0mm at Kiryu and Kawamukai catchments. The runoff outputs were 1478.8mm at Kiryu and 920. 9mm at Kawamukai. The runoff ratio was considerable larger than the past at Kiryu. Samples of precipitation and runoff water were taken for mineral components analyses. 3. The average concentration of mineral contents in precipitation were Mg: 0.17; Ca: 0.35; K: 0.38; Na: 0.48 P: 0.954; (mg

1), and in runoff were Mg: 0.18, 0.15; Ca: 0.64, 0.40; K: 0.73, 0.72; Na: 4.81, 3.89; P: 0.926, 0.024, for Kiryu and Kawamukai respectively. The mineral contents in stream water were comparatively similar in both catchments, but during the experimental period, the average concentration of mineral contents were found variable throughout the season and there were no specific trends. 4. The budget of dissolved minerals was calculated from determination of input and output. In both catchments, the annual mineral inputs were, Mg: 1.9, 1.8; Ca: 5.0, 4.8 K: 5.2, 5.2; Na: 4.7, 4.6; P: 0.5, 0.3 and annual outputs were Mg: 3.3, 1.9; Ca: 10.6, 4.1; K: 11.2, 6.7; Na: 62.5, 34.0; P: 0.5, 0.3; kg

ha for Kiryu and Kawamukai respectively. The annual outputs of potassium and sodium were strongly influenced by the amount of runoff from each catchment. In all outputs, the Kiryu catchment gave larger amounts than Kawamukai whch may suggest that the former ecosystem is better than the latter in term of mineral budgets.